This invention relates to a sample valve assembly and process for sampling a solid granular material from a container or vessel. The sample valve and process of present invention advantageously may be used for removing a catalyst sample from a process vessel such as a reactor vessel.
Effective representative sampling, for example, of catalyst beds in commercial reactors, is necessary to determine the effects of various process conditions on ultimate catalyst performance. Effects of feed poisons, temperature profile, sintering, flow distribution, attrition, crush strength, and packing height, in addition to other parameters, need to be known about individual beds of catalyst in process reactors as a means of improving performance, minimizing downtime, identifying poisons, and monitoring physical properties.
Present sampling techniques have the disadvantages of: (1) contaminating the sample: (2) changing the oxidation state of the sample: (3) changing the physical properties of the catalyst:(4) affecting the flow distribution characteristics of the reactor: (5) requiring significant downtime: and (6) potentially affecting the integrity of the reactor, such as, for example, pulling out a thermowell, taking a sample, and not being able to replace the thermowell and/or get a leak-tight seal.
Proper sampling of a catalyst is necessary to be able to gather the most usable information from a sample or series of samples. Analytical techniques are available that enable detailed analysis of catalyst morphology to the molecular level, but there is no adequate technique to enable true, unadulterated sampling of catalyst from commercial reactors. Samples taken by present methods are questionable at best and useless or damaging to the system at worst.
Some prior art catalysts, for example, Dow Type KLP catalyst commercially available from The Dow Chemical Company, in its active form is in the reduced state and is very sensitive to oxygen. In a commercial reactor in the reduced state, the catalyst may also have some hydrocarbon absorbed to its surface. The hydrocarbon, combined with its sensitivity to oxygen, makes the catalyst potentially pyrophoric if sampled in its active form. The catalyst is also sensitive to other process parameters that may affect crush strength and/or pellet integrity due to location in the reactor. Existing means of sampling, as described below, are inadequate to get a true representative sample of the catalyst.
Present art methods for sampling a catalyst such as Dow Type KLP catalyst in a commercial reactor include: (1) using a grain probe which may/can be compartmentalized and pushed through the catalyst bed of the reactor with an auger, if not just pushed into the catalyst bed by force: (2) removing an upper manway, piping connection, or thermowell of the reactor and collecting a sample: or (3) emptying the reactor and catching samples as the catalyst comes out. Each of these methods has severe limitations to enabling the taking of a true representative sample.
All of the above techniques require opening the reactor in one form or fashion, effectively exposing the catalyst to the atmosphere and, if the reactor is not adequately purged or otherwise cleared, exposing the sampling personnel to the previous contents of the reactor Probes, whether forced into the catalyst bed or "screwed" as with an auger, potentially cause damage to catalyst samples, especially the more dense packing, pelletized and/or extruded varieties of catalyst, the extent of the damage of which is not known. Forcing a probe into a catalyst bed causes attrition or crushing of the sample, resulting in obtaining a sample that is not representative of the true physical state of the catalyst in the reactor. Removal of manways, piping, or thermowells involves affecting the integrity of the reactor vessel itself, and also necessitates the vessel being reasonably cooled to allow work on the vessel.
A principal drawback of the prior art methods, in addition to being slow and labor intensive, is that samples are typically taken only from the outer perimeter of the catalyst bed, unless probe devices are used, in which case the sample suffers potential physical degradation. The above prior art methods, for the purpose of safety to sampling personnel, necessitate that the catalyst to be sampled be in some non-reactive form, such that as the vessel is opened, and a sample is taken, the catalyst does not react with the atmosphere or affect the sampling personnel in any way. In the case of dropping the catalyst charge, and sampling as the material is removed from the reactor, the relative position of the sample in the bed is estimated at best, and may be a blend of catalyst from different areas of the reactor.
It is desired to provide a sample valve and process particularly useful for allowing an operator to remove a catalyst sample from a process vessel (1) without changing the oxidation state of the catalyst sample, e.g. for catalysts that are air or moisture sensitive: (2) without damaging the physical integrity of the catalyst sample, e.g. no crushing or powdering of the sample: (3) allowing the exact position of the sample in the process vessel to be known: (4) allowing repeated sampling of the catalyst in the process vessel as the catalyst ages without affecting the integrity of the process vessel or the catalyst bed in the vessel: and (5) allowing return of the process vessel to service without leakage or contamination of the catalyst or process stream.